Electromagnetic clutches and brakes are used extensively in a variety of machines. They are used in stationary machines and on vehicles. Use on vehicles includes drives for air conditioning system compressors, air compressors, and mechanical superchargers. These clutches can take many forms. Most of the clutches include a field coil assembly, a rotor assembly and an armature assembly.
The field coil assembly is often mounted in a fixed position. A rotor assembly is rotatably mounted adjacent to the field coil in a position to form a portion of a magnetic flux path. The rotor assembly includes a drive engaging means such as a v-belt or power band engaging surface, a sprocket for a chain drive or a gear for gear drive. The rotor assembly also has an attraction surface. The armature assembly includes an armature hub, a stopper plate, an armature and a damper. The armature hub is adapted for mounting on a driven shaft. The stopper plate is attached to the armature hub and has generally radially extending arms which support the armature. There are usually three arms that support the armature in three places. The number of arms can vary. The damper includes rubber members which connect the armature to the arms of the stopper plate. The rubber members allow the armature to move into contact with the attraction surface on the rotor assembly when the field coil assembly is energized. The rubber members in the damper pull the armature away from the attraction surface when power to the field coil assembly is cut off. The damper assembly also deforms and absorbs the sudden increases in torque when the field coil assembly is energized. In addition to the high peak torques that are absorbed by the damper assembly when the field coil is energized, the damper assembly absorbs torsional vibrations from the power source and from the driven machine.
The rubber members included in the damper tend to crack, around the outside edges where the rubber contacts a metal retainer and in the center where the rubber contacts a central support post. The cracks in the rubber members lead to deterioration and a shortened useful life for the dampers and armature assemblies.
The life of the armature assemblies and the dampers, which are an integral part of the armature assemblies, can be extended by increasing the length of the metal parts to provide space for rubber filets that adhere to the metal parts when the rubber is vulcanized. The increase in the length of metal surfaces increases the axial length of the armature assembly. The increased axial length of the armature assembly is unacceptable in many vehicle installations due to the limited space available in vehicle engine compartments.